Illuminating an object in machine-vision application needs to be performed in a uniform manner over a field of view (FOV). This includes the illumination intensity and angular incidence impinging at each and every point in the FOV.
Bright field illumination (sometimes called vertical illumination or coaxial illumination) can be made uniform, with an example of a reflected Kohler illumination in a microscope working through a telecentric objective lens.
Dark field illumination of an integrating sphere can make a uniform illumination over the FOV, but is very inefficient.
There is a growing need to provide efficient dark field illuminator and methods for dark field illumination.